WASHINGTON (AP) _ Barack Obama, who hoped to use U.S. Independence Day holiday campaign stops to woo moderate voters in traditionally Republican territory, found himself instead defending against criticism that he was wavering on his Iraq war policy to win votes.

A dustup over war policy — one of the main issues separating the Illinois senator from his Republican opponent, John McCain — overshadowed Obama's town-hall meeting with veterans in Republican bastion North Dakota on Thursday. The discussion was supposed to focus on patriotism — a theme Obama has highlighted much of the week — and his plans to care for veterans. But questioning turned to Iraq policy and his impending trip there.

In a town hall meeting in Fargo, Obama left the impression that his talks with military commanders in Iraq during his upcoming visit to the war-torn country could refine his promise to remove U.S. combat troops within 16 months of taking office.

"I am going to do a thorough assessment when I'm there," he said. "I'm sure I'll have more information and continue to refine my policy."

Republicans pounced on the chance to characterize Obama as altering one of the core policies that drove his candidacy "for the sake of political expedience." He denied equally forcefully that he was shifting positions.

"There appears to be no issue that Barack Obama is not willing to reverse himself on for the sake of political expedience," said Alex Conant, a spokesman for the national Republican Party. "Obama's Iraq problem undermines the central premise of his candidacy and shows him to be a typical politician."

Obama, who is running on a promise to bring change to Washington, quickly called a second news conference to clarify, accusing McCain supporters of distorting his remarks.

The Democrat said what he learns from the military commanders will refine his policy, but "not the 16-month timetable" for withdrawing U.S. troops from combat in Iraq. He said what he learns could affect how many residual troops might be needed to train the Iraqi army and police.

"I have said throughout this campaign that this war was ill-conceived, that it was a strategic blunder and that it needs to come to an end," he said. "I have also said I would be deliberate and careful about how we get out. That position has not changed. I am not searching for maneuvering room with respect to that position."

During his presidential campaign, Obama has gone from the hard-edged, vocal opposition to Iraq that defined his early candidacy to more nuanced rhetoric that calls for the phased-out drawdown of all combat brigades that, at a rate of one or two a month, could take 16 months. He has said that if al-Qaida builds bases in Iraq, he would keep troops either in the country or the region to carry out "targeted strikes."

The exchange on Iraq underscored the stakes in a presidential race in which swing voters — courted by both Obama and McCain — are expected to play in the election.

McCain has been a vocal supporter of the Iraq war and has expressed opposition to pulling out U.S. troops until the Iraqis are able to manage their own security — positions that have opened him up to criticism by Obama.

Obama has argued that McCain offers little more than a continuation of President George W. Bush's policies and the unpopular war — arguments he hopes will sway to his camp centrist voters and moderates in states that Democratic presidential candidates have typically fared poorly.

A recent AP-Yahoo News poll finds that 15 percent of voters in the U.S. call themselves moderates and are not solidly supporting a candidate.

The Democrat was spending Friday's holiday in Montana, a state that has voted Republican for the White House for decades. Only Bill Clinton was able to carry Montana in 1992 — but only with about a third of the vote, after independent Ross Perot split the conservative vote.